Javadoc

Specifies the order for index traversal: If true (default),
the traversal is performed in ascending order; if false, the
traversal is performed in descending order.

Items with the same partition key value are stored in sorted order by
sort key. If the sort key data type is Number, the results are stored in
numeric order. For type String, the results are stored in order of UTF-8
bytes. For type Binary, DynamoDB treats each byte of the binary data as
unsigned.

If ScanIndexForward is true, DynamoDB returns
the results in the order in which they are stored (by sort key value).
This is the default behavior. If ScanIndexForward is
false, DynamoDB reads the results in reverse order by sort
key value, and then returns the results to the client.

Returns a reference to this object so that method calls can be chained
together.